1. Field
Exemplary embodiments relate to a technique for measuring a nanoscale object, and more particularly, to an optical measurement system and a method for determining a critical dimension (CD) of a nanoscale object.
2. Description of the Related Art
Recently, there has been a distinct tendency toward decreasing a critical dimension (CD) of a manufactured structure in micro lithography technology for semiconductor chip manufacturing. The CD is a measure of a nanostructure that is a test target and has a value in the range of about several tens of nanometers. At present, it is possible to obtain a CD of about 30 nm, and it is expected to reduce the CD to about 20 nm in the near future.
For semiconductor structures having very small critical dimensions (CDs), demands for a highly accurate and reliable measurement system and a fast and low-cost measurement process have increased. A conventional measurement method using a scanning electron microscope (SEM) and an atomic force microscope (AFM) has problems of relatively low speed and relatively high cost when a chip is tested using a well-known topology having a dimension slightly different from a required CD value for a semiconductor structure. For this type of measurement, optical methods based on ellipsometry and scatterometry have been developed. In particular, a well-known optical critical dimension (OCD) method is used to identify a semiconductor structure having a smaller CD than a Rayleigh limit.
Non-periodical isolated objects may be analyzed by using through-focus scanning optical microscopy (TSOM) based on analyzing a non-contrast defocused image of a registered object via a microscope optical system while scanning the object along an optical axis.